1. Field of the Invention
The present disclosure relates to a resistance generator and a load, especially to a negative resistance generator and a load including negative resistance.
2. Description of Related Art
An ideal inductor in comparison with a resistor has the feature of lossless DC (Direct Current) transmission. Therefore, in some circuit design, an inductor instead of a resistor is used as a load for the linearity improvement of circuit operation. For instance, when developing a low noise amplifier (LNA), an inductor could be used for impedance match and treated as a load such that the linearity of this amplifier would improve. However, as it is shown in FIG. 1a, an actual inductor is non-ideal and usually composed of an inductance L and a parasitic resistance Rs connected in series. If the inductance L and the resistance Rs in FIG. 1a are represented by a substitution of the inductance L and a resistance Rp connected in parallel (as shown in FIG. 1b), the relationship between the resistance Rs and the resistance Rp could be expressed with the following equation:Rp=[(ωL)2]/Rs=Rs×Q2,  (Eq. 1)in which Q=(ωL)/Rs stands for the quality factor of the inductor (when it is expressed with the inductance L and the resistance Rs connected in series). In a general case, the more the Q value is, the less the parasitic resistance Rs is, which means that the DC transmission loss becomes minor and the inductor characteristic becomes better. However, in consideration of that the Q value is positively proportional to the size of an inductor in an integrated circuit while an inductor of greater size consumes more circuit area and lead to the increase of cost, the Q value has to be determined with a dilemma of sacrificing performance or cost benefit. In addition, when an inductor is used as a load, in order to get a higher gain of signals at a specific frequency, some prior art connects the inductor with a capacitor C in parallel (as shown in FIG. 1c) so as to neutralize the AC impedance of the inductor and the capacitor when a resonance of the inductance of the inductor L and the capacitor C occurs. Under the resonance, the impedance of the load is equivalent to the parasitic resistance Rp of the inductor (as shown in FIG. 1c). Consequently, if the parasitic resistance Rp (in relation to the impedance of the load) is increased, the signal gain (e.g., a transconductance gain gm multiplied by the resistance Rp of the load) becomes higher. But if the resistance Rp is increased to improve the signal gain, the increased resistance Rp also consumes more circuit area since the resistance Rp is positively proportional to the Q value (as shown in Eq. 1), which also leads to the increase of cost. As a result, a designer again faces the dilemma of sacrificing performance or cost benefit again.
In consideration of the above, in order to improve the Q value and to increase the impedance of the load in FIG. 1c under reasonable cost, a known technique connects a load (e.g., the load in FIG. 1c) with a negative resistor composed of an active device in parallel so as to derive a better Q value with an equivalent load impedance. Unfortunately, the active region of transistor(s) under this kind of technique is inclined to enter the linear region from the saturation region due to a larger AC (Alternating Current) signal swing, which causes the linearity to be worse and therefore required to be improved as well. The mentioned prior art is illustrated in the following document: Lu, Hwang-Hsin, “WLAN 802.11a VCO design with novel tank resonator”, Department of Electrical Engineering, Chung Hua University, 2004.